Metformin Kills Cancer Stem Cells continued...

"The bulk of the cells in a tumor are cancer cells which grow but are killed
by chemotherapy," Struhl says. "But there is also a small population of cancer
stem cells, which are better able to form tumors on their own and more
resistant to chemotherapy than cancer cells. After standard chemotherapy, they
can remain and essentially regenerate the tumor, and the disease is back
again."

Different researchers have recently described new compounds that selectively
kill cancer stem cells. Whether these compounds might one day become safe and
effective cancer drugs remains to be shown.

Struhl -- who, with Harvard Medical School, holds a patent on the combined
use of metformin and low-dose chemotherapy -- says metformin is already known
to be safe and merely needs to be proven effective in human clinical
trials.

Easier Cancer Chemo With Metformin?

Another reason researchers are excited about the study findings is that
metformin and standard chemotherapy seem to make each other work better.

"Because of this synergy with chemotherapy, metformin could be used with
lower doses of chemotherapy," Struhl suggests. "Chemotherapy is quite a toxic
thing for people to deal with, and if one could lower the dose that would be
very nice."

Metformin itself has an outstanding safety record.

"This drug at low doses can be considered a very good candidate for cancer
prevention before a person has any cancer at all," Rauscher said. "The hope is
we can use a drug like metformin and continue to deplete the levels of these
inherently chemotherapy-resistant, dormant cancer stem cells."

Can Metformin Prevent Breast Cancer Recurrence?

Ligibel, who was not involved in the Struhl study, has argued that metformin
should be tested in people.

Taking her own advice, she is participating in a human study led by Canada's
national cancer institute that will test whether metformin can prevent breast
cancer from coming back after treatment. The study, which will take place at
multiple cancer centers in Canada and the U.S., has not yet begun
enrollment.

Unfortunately, Ligibel said, there are no plans for studies combining
metformin with chemotherapy. But Struhl said that because metformin is an
approved drug, such studies could begin relatively soon.

"We are hoping for researchers to actually try that experiment," Struhl
said. "The idea of using this as a combined treatment is the main point of our
paper."

"These concepts should be moved forward in clinical trials," Rauscher
agreed.